Prepreg and laminate of epoxy resin, styrene-maleic anhydride copolymer and bis-maleimidetriazine

ABSTRACT

This invention concerns a thermosetting resin system that is useful in the manufacture of high performance prepreg, laminate and composite materials as well as, prepregs, laminates and composites made from the thermosetting resin composition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/185,259 filed on Jul. 20, 2005, now U.S. Pat. No. 7,521,494, which isa continuation of U.S. application Ser. No. 10/310,418, filed Dec. 5,2002 now abandoned, which claims priority from U.S. ProvisionalApplication Ser. No. 60/337,322, filed Dec. 5, 2001, the specificationsof each of which are incorporated herein by reference in their entirety.

BACKGROUND OF THIS INVENTION

(1) Field of this Invention

This invention concerns a thermosetting resin system that is useful inthe manufacture of high performance prepreg, laminate and compositematerials as well as the prepregs, laminates and composites made fromthe thermosetting resin composition.

(2) Description of the Related Art

Plastics have certain mechanical and structural properties that can beimproved when the plastics are combined with reinforcing components.Composites formed of various fibers embedded in a polymer resin matrix,for example, are especially useful. However, such compositions aresusceptible to enormous physical property variations depending upon, forexample, the nature of the fiber used, how the fiber is utilized, andthe fiber matrix or binder. The uses for such composites range fromairframes to tennis rackets and from boat hulls to rocket motor casings,and laminates for use, for example, as multilayer printed circuit boardsin the electronics industry.

Performance requirements for composites and laminate materials arebecoming more stringent. In the electronics industry, for example, highspeed high frequency circuits require substrates with difficult toattain electrical properties, such as low dielectric loss and lowdielectric constant. Current composite materials do not meet theseelectrical requirements. In addition, other materials that may exhibitfavorable electrical properties do not possess the thermal propertiesrequired for composites and laminates. There exists a continuing need,therefore, for new composite materials having favorable thermal andelectrical properties, such as low dielectric loss and low dielectricconstant.

SUMMARY OF THIS INVENTION

This invention provides a thermosetting resin composition useful in themanufacture of high performance composite and laminate materials. Thethermosetting resin composition comprises: at least one epoxy resin; atleast one styrene maleic anhydride copolymer; and at least onebis-maleimidetriazine resin.

This invention also provides prepregs, laminates and compositesmanufactured from the disclosed thermosetting resin compositions.

DESCRIPTION OF THE CURRENT EMBODIMENT

This invention provides thermosetting resin compositions useful in themanufacture of high performance composite materials, and prepregs,laminates and composites manufactured therefrom. The compositions areparticularly useful in the preparation of laminates having lowdielectric constants and low dielectric loss (“low loss”). Theseelectrical properties help solve signal speed and signal integrityproblems encountered with high speed analog digital applicationsmanufactured using laminates with prior art resin systems.

Laminate materials manufactured with the thermosetting resincompositions of the present invention can have low and flat dielectricloss (≦0.01) and low dielectric constant (≦4) at high frequency range of2 GHz to 10 GHz, at comparatively low cost. “Flat dielectric loss” meansthat the dielectric loss is essentially constant over a range offrequencies. The compositions of this invention may have a dielectricloss as low as ≦about 0.01 over a frequency range of from 2 to 10 GHz.(As is understood by those skilled in the art, dielectric loss andconstant depend on resin content and can additionally depend on otherfactors, such as the substrate used in a laminate). In addition tohaving favorable electrical properties, prepregs prepared from thecompositions of this invention are also non-tacky and easy to process.

The thermosetting resin composition includes the following ingredients:(1) at least one epoxy resin; (2) at least one styrene maleic anhydride;and (3) a bis-maleimidetriazine resin. The composition optionallyincludes one or more of the following: (4) a filler; (5) a toughener;(6) an accelerator; (7) a flame retardant; (8) a solvent; and/or (9)other additives.

(1) The Epoxy Resin

The term “epoxy resin” in this context refers to a curable compositionof oxirane ring-containing compounds as described in C. A. May, EpoxyResins, 2nd Edition, (New York & Basle: Marcel Dekker Inc.), 1988.

The epoxy resin is added to the resin composition in order to providethe desired basic mechanical and thermal properties of the cured resinand laminates made there from. Useful epoxy resins are those that areknown to one of skill in the art to be useful in resin compositionsuseful for electronic composites and laminates.

Examples of epoxy resins include phenol types such as those based on thediglycidyl ether of bisphenol A (“Bis-A epoxy resin”), on polyglycidylethers of phenol-formaldehyde novolac or cresol-formaldehyde novolac, onthe triglycidyl ether of tris(p-hydroxyphenol)methane, or on thetetraglycidyl ether of tetraphenylethane, or types such as those basedon tetraglycidylmethylenedianiline or on the triglycidyl ether ofp-aminoglycol; cycloaliphatic types such as those based on3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate. The term“epoxy resin” also includes within its scope reaction products ofcompounds containing an excess of epoxy (for instance, of theaforementioned types) and aromatic dihydroxy compounds. These compoundsmay be halogen substituted.

Preference is given to epoxy resins which are derivatives of bisphenol A(“Bis-A epoxy resin”), particularly FR4. FR4 is made by an advancingreaction of an excess of bisphenol A diglydicyl ether withtetrabromobisphenol A. Mixtures of epoxy resins with bismaleimide resin,cyanate resin and/or bismaleimide triazine resin can also be used.

It should be noted that epoxy resins are generally represented by asingle, unequivocal structural formula. The skilled person will knowthat this should be taken to include deviating products resulting fromside reactions occurring during epoxy resin preparation. As these sideproducts constitute a normal component of cured epoxy resins, theylikewise constitute a normal component of the resins according to thisinvention. Epoxy resins are present in the composition of this inventionin an amount from about 8% to about 26%, and preferably from about 10 toabout 23%, based on 100% by weight solids of the composition.

Bisphenol A (BPA) and/or bisphenol A diglycidyl ether (BPADGE) canoptionally be included with the epoxy resin as co-crosslinking agents.Both the BPA and the BPADGE may optionally be brominated, i.e.substituted with one or more bromine atoms. Resin systems incorporatingoptionally brominated bisphenol A and optionally brominated bisphenol Adiglycidyl ether that are useful in the present invention are describedin U.S. Pat. No. 6,509,414, which is incorporated herein by reference inits entirety. In the present invention, the aromatic moieties of BPA andBPADGE are preferably substituted with two bromine atoms, to givetetrabromobisphenol A (TBBA) and tetrabromobisphenol A diglycidyl ether(TBBADGE), respectively. Optionally brominated novolacs can also be usedas co-cross-linking agent. Brominated co-crosslinking agents arepreferred because of their flame retarding properties.

The desired resin properties determine the amount of optionallybrominated BPA and optionally brominated BPADGE to be incorporated intothe resin. According to this invention, for instance, it hassurprisingly been found that the Tg of epoxy resins cross-linked withSMA can be increased substantially by the use of at least 5% by weightof BPA. Most surprisingly of all, it is now possible, as indicatedabove, to obtain resins having glass transition temperatures of 130° C.and higher even with simple difunctional epoxy compounds. When aco-crosslinking agent is used, it is generally present in amount ofabout 5% to about 60%, preferably about 15% to about 55%, based on 100%by weight solids of the composition. In a preferred embodiment, thecomposition of this invention contains both TBBA and TBBADGE. In thispreferred embodiment, the TBBA is present in an amount of from about 3%to about 21 wt %, preferably from about 6% to about 19%, and the TBBADGEis present in amount of from about 9 wt % to about 30 wt %, preferablyfrom about 11 wt % to about 26 wt %, each based on 100% by weight solidsof the composition.

(2) Styrene Maleic Anhydride Copolymer

The thermosetting resin compositions of this invention includes one ormore styrene maleic anhydride compounds (SMA). SMA improves the thermaland electrical properties of the resulting cured polymer and productsmade therefrom by reacting with unreacted elastomer ingredients andby-products.

Copolymers of styrene and maleic anhydride have been described, interalia, in Encyclopedia of Polymer Science and Engineering Vol. 9 (1987),page 225. Within the framework of this invention the term “copolymer”likewise refers to SMA or mixtures of SMA. Copolymers of styrene andmaleic anhydrides (SMA) are commercially available in two types. Type 2comprises mostly high-molecular weight copolymers (MW generally higherthan 100,000, for instance, 1,000,000). These are in factthermoplastics, which are unsuitable for use in the manufacture ofprepregs. Moreover, because of their low anhydride content (5-15%) theyare not particularly suitable for use as a crosslinking agent for epoxyresin either. The type 1 SMA copolymers, on the other hand, which have amolecular weight in the range of about 1400 to about 50,000 and ananhydride content of more than 15% by weight, are especially suited foruse in compositions of this invention. Preference is also given to SMAcopolymers having a molecular weight in the range of 1400 to 10,000.Examples of such copolymers include the commercially available SMA 1000,SMA 2000, SMA 3000, and SMA 4000. These copolymers have a styrene maleicanhydride ratio of 1:1. 2:1, 3.1, and 4:1, respectively, and a molecularweight ranging from about 1400 to about 2000. Mixtures of these SMAs mayalso be used. SMA polymers are present in the thermosetting resincompositions of this invention in an amount from about 10% to about 26%,preferably from about 15 to about 23%, based on 100% by weight solids ofthe composition. In one preferred embodiment, the amount of epoxy resinexceeds the amount of SMA in order to provide an excess of functionalityof the epoxy over the SMA. hi this embodiment, the weight ratio of epoxyresin to SMA copolymer is preferably about 2:1 to about 1.5:1(epoxy:SMA).

(3) Bis-maleimidetriazine resins

The thermosetting resin compositions of this invention further includesa Bis-maleimidetriazine resin (BT). BT resins are commercially availablefrom Mitsubishi. Bis-maleimidetriazine resins are present in thethermosetting resin compositions of this invention in an amount fromabout 15% to about 50%, preferably from about 25 to about 40%, based on100% by weight solids of the composition.

(4) The Optional Filler

One or more fillers can optionally be added to the resin compositions ofthis invention to improve chemical and electrical properties of thecured resin. Examples of properties that can be modified with fillersinclude, but are not limited to, coefficient of thermal expansion,lowering CTE, increasing modulus, and reducing prepreg tack.Non-limiting examples of useful fillers, include particulate forms ofTeflon®, talc, quartz, ceramics, particulate metal oxides such assilica, titanium dioxide, alumina, ceria, clay, boron nitride,wollastonite, and mixtures thereof. Preferred fillers include calcinedclay or fused silica. Another preferred filler is fused silica. Yetanother preferred filler is silane treated silica. More preferably, thesilane treated filler filler is fused silica treated with epoxy silane.When used, fillers are present in the thermosetting resin compositionsof this invention in an amount from about 0% to about 20%, preferablyfrom about 0 to about 10%, based on 100% by weight solids of thecomposition.

(5) The Optional Toughener

The thermosetting resin compositions of this invention may include oneor more tougheners. The tougheners are added to the resin compositionsto improve the drillability of the resulting composites and laminates.Useful tougheners include methyl methacrylate/butadiene/styrenecopolymer, methacrylate butadiene styrene core shell particles, andmixtures thereof. A preferred toughener is methacrylate butadienestyrene core shell particles, which is available from Rohm & Haas (100Independence Mall West, Philadelphia, Pa.), sold under the trade nameParaloid®. When used, tougheners are present in the thermosetting resincompositions of this invention in an amount from about 1% to about 5%,preferably from about 2 to about 4%, based on 100% by weight solids ofthe composition.

(6) Accelerators

One or more accelerators are typically added to the composition tocrosslink the resins and to enhance the rate of resin cure. Theaccelerators chosen may be any accelerators that are know to speed upthe rate of thermosetting resin cure. As suitable accelerators may bementioned imidazoles, more particularly alkyl substituted imidazolessuch as 2-methylimidazole and 2-ethyl-4-methylimidazole,2-phenylimidazole, 2-phenyl, 4-methylimidazole. Other suitableaccelerators include tertiary amines, e.g. benzyldimethylamine and 4,4′and 3,3′diaminodiphenylsulphone. One preferred accelerator is2-ethyl-4-methylimidazole. The amount of accelerator used is dependenton the type of epoxy resin, the type of cross-linking agent, and thetype of accelerator. Employing a too large amount of accelerator willlead to a too highly reactive resin system. The skilled person caneasily determine the amount of accelerator needed to provide a resinsystem that is sufficiently reactive to allow ready processing intoprepregs. In general, such amount will be between 0 01 and 5% by weightof accelerators, calculated on the overall weight of epoxy resin andco-crosslinking agent present in the composition. In many cases thiswill be the 0.01-0.05% by weight range. The resin gel is dependent onthe type anal amount of accelerator, the type and amount of solvent, andthe type of prepreg to be manufactured. In the specific case of 2methylimidazole (2MI) being used as a accelerator, it is preferred notto use more than about 0.05% by weight of 2MI. By way of generalguideline it can be said that it is advisable not to have a varnish geltime of less than 120 seconds.

(7) Optional Flame Retardants

The thermosetting resin compositions of this invention may include oneor more flame retardants. Any flame retardant that is known to be usefulin resin compositions used to manufacture composites and laminates maybe used. Examples of useable flame retardants include, but are notlimited to, halides of glycidyl etherified bifunctional alcohols,halides of novolac resins such as bisphenol A, bisphenol F,polyvinylphenol or phenol, creosol, alkylphenol, catecohl, and novolacresins such as bisphenol F, inorganic flame retardants such as antimonytrioxide, red phosphorus, zirconium hydroxide, barium metaborate,aluminum hydroxide, and magnesium hydroxide, and phosphor flameretardants such as triphenyl phosphine, tricresyl phosphine,triethylphosphate, cresyldiphenylphosphate, xylenyl-diphenyl phosphate,acid phosphate esters, phosphate compounds containing nitrogen, andphosphate esters containing halides. Flame retardants are present in thethermosetting resin compositions, of this invention in an amount of fromabout 3 to about 9%, preferably from about 4 to about 8%, based on 100%by weight resin solids of the composition.

Another optional flame retardant is decabromodiphenylethane, which hasthe following structure:

Decabromodiphenylethane is commercially available, for example, fromAlbemarle Corporation (451 Florida St., Baton Rouge, La. 70801). TheAlbemarle product is sold as Saytex™ 8010. Decabromodiphenylethane hasbeen unexpectedly found to be easily dispersed in the resin composition.Decabromodiphenylethane also has the unexpected and synergistic resultof significantly improving dielectric properties of the cured resin. Asa result, the flame retardant can be included in the resin compositionof this invention in amounts far greater than is necessary for a flameretardant in order to also enhance the dielectric properties of thecured resin. When decabromodiphenylethane is used as the flameretardant, it is preferably present in the thermosetting resincompositions of this invention in an amount of from about 10% to about50%, more preferably from about 20% to about 45%, based on 100% byweight resin solids of the composition. When a brominated flameretardant is used, it is preferably present in an amount sufficient toprovide a total bromine content to the composition of about 8% to about30%, preferably about 10 to about 20%, based on 100% by weight solids ofthe composition.

(8) Solvents

One or more solvents are typically incorporated into the thermosettingresins of this invention in order to provide resin solubility, controlresin viscosity, and in order to maintain the resin ingredients in asuspended dispersion. Any solvent known by one of skill in the art to beuseful in conjunction with thermosetting resin systems can be used.Particularly useful solvents include methylethylketone (MEK), toluene,dimethylformamide (DMF), or mixtures thereof. The choice of solvent isoften dictated by the resin curing method. When the resin is cured withhot air, then ketones are typically the preferred solvent. When theresins are IR cured, then a mixture of ketones and toluene is typicallypreferred. When used, solvents are present in the thermosetting resincompositions of this invention in an amount of from about 20% to about50% as a weight percentage of the total weight of the composition.

Optionally, the thermosetting resin composition of the present inventionmay further contain other additives such as defoaming agents, levelingagents, dyes, and pigments. For example, a fluorescent dye can be addedto the resin composition in a trace amount to cause a laminate preparedtherefrom to fluoresce when exposed to UV light in a board shop'soptical inspection equipment. A useful fluorescent dye is a highlyconjugated diene dye. One example of such a dye is UVITEX® OB(2,5-thiophenediylbis(5-tert-butyl-1,3-benzoxazole), available from CibaSpecialty Chemicals, Tarrytown, N.Y.

One useful composition of this invention has the following formulation:

HIGH PERFORMANCE ELECTRICAL LAMINATE FORMULATION Range Preferred AmountsIngredients (wt %) (wt %) Epoxy Resin Bis-A Epoxy Resin 10-26 15-23Brominated Bis-A Epoxy (TBBADGE)  9-30 13-26 Tetrabromobisphenol A(TBBA)  7-21 11-19 SMA 10-26 15-23 Toughener 1-5 2-4 Methacrylatebutadiene styrene core shell particles (Paraloid 2591) Accelerator0.05-1.0  0.2-0.5 BT Resin 15-50 25-40 Filler  0-20  0-10

The ingredients are suspended in a DMF, MEK or MEK/DMF solvent in aratio ranging from about 50-80 wt % solids to 50-20 wt % solvent andpreferably about 70 wt % solids to about 30 wt % solvent.

The thermosetting resin compositions of this invention are useful formaking prepregs in a continuous process. Prepregs are generallymanufactured using a core material such as a roll of woven glass webwhich is unwound into a series of drive rolls. The web then passes intoa coating area where the web is passed through a tank which contains thethermosetting resin system of this invention, solvents and othercomponents. The glass web becomes saturated with the resin in thecoating area. The resin saturated glass web is then passed through apair of metering rolls which remove excess resin from the resinsaturated glass web and thereafter, the resin coated web travels thelength of a drying tower for a selected period of time until the solventis evaporated from the web. A second and subsequent coating of resin canbe applied to the web by repeating these steps until the preparation ofthe prepreg is complete whereupon the prepreg is wound onto roll.

Lamination process typically entail a stack-up of one or more prepreglayers between one or two sheets of conductive foil (such as copperfoil). Lamination methods and parameters may vary widely, and aregenerally well known to the person of ordinary skill in the art. In atypical cure cycle, the stack is maintained at a pressure of about 40psi to about 900 psi and under a vacuum of about 30 in/Hg. The stacktemperature is raised from about 180° F. to about 375° F. over a periodof about 20 minutes. The stack remains at a temperature of about 375° F.for 75 minutes after which the stack is cooled from a temperature of375° F. to a temperature to 75° F. over a 20 minute period.

In another process for manufacturing laminates, thermosetting resins ofthis invention are premixed in a mixing vessel under ambient temperatureand pressure. The viscosity of the pre-mix is ˜600-1000 cps and can beadjusted by adding or removing solvent from the resin. Fabric substrate(typically but not limited to E glass) is pulled through a dip tankincluding the premixed resin, through an oven tower where excess solventis driven off and the prepreg is rolled or sheeted to size, layed upbetween Cu foil in various constructions depending on glass weave style,resin content & thickness requirements.

The thermosetting resin mix can also be coated directly on Cu substrate(RCC—resin coated Cu) using slot-die or other related coatingtechniques.

The following examples are illustrative of various aspects of theinvention but do not serve to limit its scope.

EXAMPLES Example 1 Electrical and Thermal Properties

In this example, the electrical and thermal properties of castings ofthe thermosetting resin compositions according to the invention weremeasured. The ingredients of the composition and their amounts arelisted in Tables 1 and 2. Table 1 is an unfilled resin composition.Table 2 is a filled resin composition. DMF was used as solvent toprovide a total solids content of about 67% for the unfilled resincomposition and about 71% for the filled resin composition.

TABLE 1 Unfilled Resin Composition Amount Ingredient (percentage of 100%solids) Epoxy resin Bis A epoxy 17% TBBA 11% TBBADGE 17% SMA 22.5% BTresin 30% 2-ethyl-4-methylimidazole 0.08% Toughener (Paraloid ®) 2.4%Fluorescent dye (Uvitex ® OB) 0.02%

TABLE 2 Filled Resin Composition Amount Ingredient (percentage of 100%solids) Epoxy resin Bis A epoxy 13% TBBA 8.5% TBBADGE 14% SMA 18% BTresin 24% 2-ethyl-4-methylimidazole 0.07% Toughener (Paraloid ®) 1.9%Fluorescent dye (Uvitex ® OB) 0.02% Silica filler 20%Physical and electrical properties of the unfilled and filled resincompositions are provided in Table 3. The data show that the resincomposition exhibit very good Tg values and provides maximum Dk and Dfvalues of 3.03 and 0.0085, respectively, at high frequency ranges ofabout 1 GHz.

TABLE 3 Physical and electrical properties of filled and unfilled resincompositions. DK @ 1 Df @ 1 CTE CTE Tg GHz GHz Tg-288 23-288 DSC DMA(after post (after post RESIN (ppm/° C.) (ppm/° C.) ° C. Tg G′ bake)bake) Unfilled 193 107 197 175 3.43 0.0085 filled 172 99.6 195 187 3.030.0067

It is contemplated that various modifications may be made to thecompositions, prepregs, laminates and composites of the presentinvention without departing from the spirit and scope of the inventionas defined in the following claims.

1. A prepreg comprising: a substrate impregnated with a thermosettingresin the thermosetting resin including: (1) at least one epoxy resin;(2) at least one styrene-maleic anhydride copolymer; (3) from about 15to about 50 wt % of at least one bis-maleimidetriazine resin; and (4)decabromodiphenylethane.
 2. The prepreg of claim 1 wherein thermosettingresin composition of claim 1 including an accelerator.
 3. The prepreg ofclaim 2 wherein the accelerator is an imidazole.
 4. The prepreg of claim1 wherein the thermosetting resin includes a filler.
 5. The prepreg ofclaim 4 wherein the filler is selected from the group consisting ofteflon, talc, quartz, ceramics, particulate metal oxides, silica,titanium dioxide, alumina, ceria, clay, boron nitride, wollastonite, andmixtures thereof.
 6. The prepreg of claim 1 wherein the thermosettingresin includes: an epoxy resin comprising 15-23 weight percent of abisphenol-A epoxy resin, 13-26 weight percent of brominated bisphenol Adiglycidyl ether, and 11-19 weight percent of tetrabromobisphenol A;15-23 weight percent of an styrene-maelic anhydride copolymer; 2-4weight percent of methacrylate butadiene core shell particles; 0.2-0.5weight percent of an accelerator; 25-40 weight percent of abismaleimidetriazine resin; and 0-10 weight percent of a filler.
 7. Theprepreg of claim 1 wherein the substrate is a woven glass material. 8.The prepreg of claim 1 wherein the thermosetting resin composition is atleast partially cured.
 9. A laminate including one or more pregregs ofclaim 1 and one or more sheets of conducting foil.
 10. The laminate ofclaim 9 including at least one prepreg positioned between sheets ofconducting foil.
 11. The laminate of claim 9 including at least onesheet of conducting foil positioned between prepreg sheets.